A Phylogeny of Piptochaetium (Poaceae: Pooideae: Stipeae) and related genera based on a combined analysis including trnL-F, rp116, and morphology

The tribe Stipeae occurs in temperate and warm temperate grasslands of Eurasia, Australia, and America. Although generic circumscription within the tribe has recently undergone significant changes, the American genus Piptochaectium has been clearly defined by morphological and anatomical characters. It includes 36 species and 2 varieties, most of them widely distributed in temperate grasslands of South America. Phylogenetic analyses were conducted in Piptochaetium and allied genera of the Stipeae, in order to test the monophyly of the genus, re-examine infrageneric taxa, and analyze relationships among species of this genus and allied genera of Stipeae. Two chloroplast molecular markers, trnL-F and rpl16, as well as morphology were used. Topology between morphological and molecular data mainly differs in the relationships of Piptochaetium with Anatherostipa and Piptatherum. Molecular and combined analyses yielded two major clades in the tribe: the x = 11 Clade with Piptochaetium, Aciachne, Anatherostipa, and Jarava vaginata, and the Aneuploid Clade with Jarava, Nassella, and Piptatherum. Monophyly of Piptochaetium was confirmed by morphological and total evidence (morphology and DNA data) analyses. Monophyly of sect. Podopogon, sect. Piptochaetium and Nassella were only supported by the total evidence analysis. Circumscription of Jarava is also discussed.